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The collision-induced dissociation (CID), electron capture (EC), and dissociative capture (DC) processes in H2+ + He collision are investigated by the quantum-mechanical molecular-orbital close-coupling method in the energy range of 0.02-10 keV/u. The studies are based on the ab initio calculation of the molecular structure data for different H2+ alignments with respect to the incident beam direction. The cross sections are compared with the available experimental and theoretical results. The CID process dominates the EC and DC processes. The CID cross sections sensitively depend on the molecular orientations at the time of dissociation in the energy region considered. Dissociation is found to be more likely to occur when the molecular axis is aligned perpendicular to the collision trajectory. The rotational couplings play an important role in dissociation processes. [ABSTRACT FROM AUTHOR]

The x-ray spectra resulting from single-electron capture in charge-exchange collisions of Nel0+ with He and Ne atoms are investigated for the projectile energy of 4.54 keV/u using the two-center atomic-orbital close-coupling method. The calculated spectra of the Ne9+ ion produced in Ne10+ + He and Nel0+ + Ne election-capture collisions have, generally speaking, the same level of agreement with experimental measurements as those calculated previously by the classical trajectory Monte Carlo method, indicating that multi-electron-capture processes, particularly in the case of the Nel0+ 4- Ne system, significantly affect the considered spectra. The effects of two-electron capture on the spectral line intensity have been demonstrated qualitatively by using the binomial statistics and independent particle model for the target outer-shell electrons. The role of multi-electron-capture processes in the Nel0+ 4- Ne collision system needs further attention. [ABSTRACT FROM AUTHOR]

Single-electron capture (SEC) and double-electron capture (DEC) processes in collisions of ground state N3+ (2s² ¹S) ions with He are investigated by using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method. The ab initio adiabatic potentials, radial and rotational coupling matrices utilized in QMOCC calculations, are obtained from the multireference single- and double-excitation configuration interaction approach. Total and state-selective SEC and DEC cross sections are presented in the low-energy range from 0.1 eV to 15 keV (i.e., 0.007 eV/u -1.07 keV/u) and rate coefficients in the temperature range from 104 to 107 K. Our results indicate that the SEC dominates the charge-transfer process in the considered energy region of this collision system and the SEC cross sections are nearly constant in the relatively high-collision energy region, while the DEC cross sections are about 2 orders of magnitude smaller. It is found that, for the SEC processes, in the dominant mechanisms, electrons are captured to exoergic channels N2+ (2s2p² ²D, ²S), and for the DEC processes, they are captured to N+ (2s²2p² ¹D, ¹S). Our calculations also reveal that rotational couplings become important at E > 10 eV/u for SEC and E > 200 eV/u for DEC processes. [ABSTRACT FROM AUTHOR]

Polarization spectroscopy of He+(nl) ion produced in He2+-H(1s) collisions in a Debye plasma is studied by the two-center atomic orbital close-coupling (TC-AOCC) method in the energy range 1-200 keV/u. The atomic orbitals and electron binding energies of atomic states are calculated within the Debye-Hückel approximation of the screened Coulomb potential and used in the AOCC dynamics formalism to calculate the magnetic substate-selective electron-capture cross sections. It is demonstrated that the screening of Coulomb interactions affects the entire collision dynamics and the magnitude and energy behavior of m-state-selective cross sections. The changes in magnetic substate-selective electron-capture cross sections when the interaction screening varies introduce dramatic changes in the polarization spectroscopy with respect to the unscreened interaction case. The magnetic substate-selective electron-capture cross sections, as well as the polarization degrees for the 2p 2P3/2-1s 2S1/2,3p 2P3/2-2s 2S1/2,3d 2D5/2-2p 2P3/2, and 3d 2D3/2-2p 2P1/2 transitions in the He+ ion produced in this collision system, are presented and discussed for a number of representative screening parameter values. [ABSTRACT FROM AUTHOR]

The electron capture process for the Si3+(3s) + H(ls) collisions is investigated by the quantum-mechanical molecular orbital close-coupling (MOCC) method and by the two-center atomic orbital close-coupling (AOCC) method in the energy range of 10-5-10 keV/u and 0.8-200 keV/u, respectively. Total and state-selective cross sections are presented and compared with the available theoretical and experimental results. The present MOCC and AOCC results agree well with the experimental measurements, but show some discrepancy with the calculations of Wang et al. [Phys. Rev. A 74, 052709 (2006)] at E > 40 eV/u because of the inclusion of rotational couplings, which play important roles in the electron capture process. At lower energies, the present results are about three to five times smaller than those of Wang et al. due to the difference in the molecular data at large internuclear distances. The energy behaviors of the electron capture cross sections are discussed on the basis of identified reaction mechanisms. [ABSTRACT FROM AUTHOR]

Electron emission from the single-electron capture with simultaneous single ionization in 30 keV/u He2+ on argon was investigated using a reaction microscope, providing the electron energy spectra and momentum distributions. Intensive peaks for electrons with near-zero kinetic energies have been observed. It is demonstrated that mechanisms contributing to the electron emission include direct transfer ionization (DTI), double-electron capture with autoionization (DECA), and single-electron capture with autoionization (SECA) of target. Comparison of resonance energies shows that Ar+ ions in SECA decay mainly through the 3s3p53d states by emitting Auger electrons, and He** in DECA decay through the 2l2l′ states. The dependence of electron emission on the transverse momentum exchange has been studied. In the transfer ionization channel studied here, the DTI process dominates the electron emission, and no saddle point electron mechanism has been found. [ABSTRACT FROM AUTHOR]

The electron transfer mechanism was investigated for the single-electron-capture process in 3-keV/u ArAr8+ -He collisions with cold target recoil ion momentum spectroscopy. The different state-selective electron capture processes were identified for one 1 s electron of He capture into 4 s, 4 p, 4 d - 4 f, and 5 s - 5 p states of ArAr8+. We observed that 1 s to 4 s capture mainly happens at small transverse recoil ion momentum, while 1 s to 4 p capture mainly happens at large transverse recoil ion momentum. By comparing the measured projectile scattering angle distributions to the theoretical calculations, it is suggested that 1 s to 4 s and 1 s to 4 p state-selective capture processes are mainly caused by radial and rotational coupling effects, respectively, and the 4 p ± 1 quantum states are preferred. [ABSTRACT FROM AUTHOR]